Known electronic tachometers presently on the market are not capable of quick and simple determination of the average speed of a cyclically loaded rotating shaft, especially with the accuracy and resolution required in order to determine the power output of the rotating shaft. However, there are many circumstances where accurate, high resolution determination of a cyclically loaded rotating shaft's average speed is necessary. For instance, in common textile processes, motor shafts are often conventionally connected to a cyclic time varying load, and accurate average speed measurement over the cycle is necessary in such situations in order to obtain an accurate determination of motor power output. Accurate determination of motor power output allows adjustment to the motors or processes in order to more effectively utilize electrical energy. Tachometers presently on the market are generally either of the analog variety or are of the one or two second sampling rate type. The analog tachometers are difficult to read with the accuracy and resolution required in power calculations, and while the sampling rate types have greater accuracy, they are capable of measuring the average speed only for a one or two second period, and not over an entire cyclic period.
According to the present invention, a method is provided for electronically simply and easily determining the average speed of a cyclically loaded rotating shaft, and an electronic tachometer having an accuracy of .+-.0.05%, .+-.1 count (when the time span is 2 seconds) with a resolution of 0.1 rpm, is provided for practicing the method. In this way, a simple, accurate average speed measurement over a cycle is obtained suitable for use in motor power output calculations. According to the present invention, average shaft speed may be accurately determined over an adjustable cycle span of from 2 to 120 seconds, fulfilling all the necessary requirements for motor power calculations especially in the textile processing environments. Another application of the invention is in determining yield on spinning frames.
According to the method of the present invention, the average speed of a cyclically loaded rotating shaft is determined by the steps of electronically counting the revolutions of the shaft, providing a highly time-regular pulse stream, simultaneously with a counting of the shaft revolutions counting the number of pulses in the highly time-regular pulse stream over a time span between 2 and about 120 seconds, dividing the number of revolutions counted by the number of time pulses, during the 2 to about 120 seconds time span to determine average speed, and digitally displaying the average speed determined. Restarting of the revolution and time pulse counting cycles takes place during dividing of the stored, counted revolutions and time pulses. The accuracy of the average speed displayed is .+-.0.05%, .+-.1 count when the time span is 2 seconds (accuracy increasing as the time span increases), with a resolution of about 0.1 rpm with a capability of measuring maximum average speed of about 5000 rpm for a 120 second time span (with maximum average speed determinable increasing as the time span decreases). The average speed so determined is suitable for use in calculating motor power output in order to ultimately achieve greater energy efficiency of the motors.
The electronic tachometer according to the present invention comprises means for sensing each revolution of a rotating shaft, means for electronically counting and storing the number of revolutions of the shaft, means for electronically generating a highly time-regular pulse stream, means for counting and storing the number of pulses in the highly time-regular pulse stream over a given time span simultaneously with a counting of the number of shaft revolutions, means for controlling the given time span so that it is adjustable to a time span within the range of 2 to about 120 seconds, means for electronically dividing the number of revolution pulses counted by the number of time pulses counted during the given time span to determine the shaft average speed, and means for digitally displaying average speed so determined. While a wide variety of solid state components are utilizable in practicing the invention, the time-regular pulse stream generating means preferably comprises a crystal stabilized oscillator circuit; a time span generating means comprises a programable timer with a variable resistor providing adjustment of the time span; the shaft revolution and time pulse counting means preferably comprise BCD counters; and the dividing means preferably comprises a calculator chip. A pulse shaper is preferably disposed between the sending means and the shaft revolution counting means, and a cycle counter is provided for manipulating the stored revolution and time count data into the dividing means, the cycle counter preferably comprising a plurality of shift registers.
It is the primary object of the present invention to provide a method and apparatus for the determination of the average speed of a cyclically loaded rotating shaft with sufficient accuracy and resolution to be useful in calculating power output of the rotating shaft. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.